Instrument for testing liquid samples



FIG. 1 is a front perspective view of an instrument for testing liquid samples showing my new design;

FIG. 2 is a right side elevational view thereof;

FIG. 3 is a rear perspective view thereof;

FIG. 4 is a rear elevational view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for an instrument for testing liquid samples, as shown and described. 